In vitro autoradiographical localization of melatonin binding sites in the caprine brain

Abstract

The recent development of a specific 2-[125I]-iodo-melatonin ligand has led to the identification of 125I-melatonin binding sites in the brains of numerous mammalian species. The present study reports the localization of 125I-melatonin binding sites in the brain of the dairy goat. Six previously untreated female goats, aged 5-7 years, were culled under natural light between 0900 and 1100. Brains and pituitaries were immediately dissected out and frozen on dry ice. Both transverse and sagittal sections of frozen brain were cut 20 microns thick and thaw-mounted onto gelatin-coated slides. Three consecutive sections were cut at intervals throughout the brain, mounted onto three slides, labeled A, B, and C, and thusly treated: (A) incubated for 2 hr at room temperature in a 50 pM solution of 125I-melatonin; (B) incubated for 2 hr at room temperature in a 50 pM solution of 125I-melatonin plus 1 microM cold melatonin; (C) fixed in Clarke's fluid and stained with toluidine blue. After incubation, A (specific) and B (nonspecific) slides were washed three times in ice-cold Tris-HCl buffer (pH 7.7), air-dried, exposed to an X-ray film for 2 weeks at -20 degrees C, and then fixed and stained. Specific 125I-melatonin binding sites were found in the pars tuberalis (PT), the area of the suprachiasmatic nucleus (SCN), preoptic area (POA), fornix/mediolateral septal areas, hippocampus, and the cerebral cortex. 125I-melatonin did not bind in the hindbrain, midbrain, neurohypophysis, pars intermedia or pars distalis of the adenohypophysis, or the pineal.

Melatonin Binding Sites in the Ovine Brain and Pituitary: Characterization During the Oestrous Cycle

“…The presence of specific 2-[ '251]iodomelatonin binding sites in the hippocampus is intriguing. Although comparative studies of this region of the brain are limited in number, high affinity labelling has been observed in the hippocampal formation of the laboratory rat (7; Williams, unpublished observations), red deer (46) and goats (47). The hippocampus is functionally linked through bidirectional connections to the septohypothalamic area and to the higher brain centres of the cerebral cortex (48), however, the significance of the specific binding sites identified in each of these areas remains to be determined.…”

Seasonality and Melatonin Receptors in the Pars tuberalis in Some Long Day Breeders

“…Since these initial stud ies, melatonin receptors have been demon strated in the PT of all mammalian species studied so far by autoradiography: rat [6][7][8]. Syrian hamster [7,9,10], Siberian hamster [7,11], European hamster [6], ferret [12], rabbit [13], sheep [14][15][16][17][18][19], goat [20], western spotted skunk [21], white-footed mouse [22], ground squirrel [23], mink [24,25], vervet monkey [26], baboon [26], rhesus monkey [27], hedge hog [28], Norwegian brown rat [29], guinea pig [29], dormouse, garden dormouse and jer boa [Masson-Pevet, unpubl. data].…”

Delayed rectifier outward K+ current mediates the migration of rat cerebellar granule cells stimulated by melatonin

“…The actions of MT can be ascribed to its interaction with specific receptors (Witt‐Enderby and Li 2000). These receptors, mediating the actions of MT, are now classified into MT 1 R, MT 2 R and MT 3 R. They have been identified and characterized in a number of tissues, such as hippocampus, cerebral and cerebellar cortex, and retina (Williams 1989; Blazynski and Dubocovich 1991; Deveson et al. 1992).…”

“…The actions of MT can be ascribed to its interaction with specific receptors (Witt-Enderby and Li 2000). These receptors, mediating the actions of MT, are now classified into MT 1 R, MT 2 R and MT 3 R. They have been identified and characterized in a number of tissues, such as hippocampus, cerebral and cerebellar cortex, and retina (Williams 1989;Blazynski and Dubocovich 1991;Deveson et al 1992). While MT 1 R and MT 2 R cloned from different species have been shown to be G protein-coupled (Reppert et al 1995), it is still uncertain whether MT 3 R matches all the criteria for classifying as a G protein-coupled receptor (Dubocovich et al 2003).…”